1. Field of the Invention
The present invention relates to a semiconductor sensor device for measuring a physical amount such as temperature or pressure, and more particularly, to a two-terminal semiconductor sensor device to be connected to an external device through only two external terminals.
2. Description of the Related Art
A conventional two-terminal semiconductor sensor device is described taking a temperature sensor as an example. FIG. 6 is a circuit diagram illustrating a conventional two-terminal semiconductor temperature sensor device.
An NPN bipolar transistor 91 generates a voltage Vbe1 between a base and an emitter thereof based on temperature. An NPN bipolar transistor 92 also generates a voltage Vbe2 between a base and an emitter thereof based on temperature at the time. Then, a differential voltage ΔVbe between the voltage Vbe2 and the voltage Vbe1 is generated across a resistor 93. Based on the differential voltage ΔVbe and a resistance of the resistor 93, the resistor 93 causes a current based on the temperature at the time to flow therethrough. The current is allowed to flow through a PNP bipolar transistor 94, the NPN bipolar transistor 91, and the resistor 93. The current is also allowed to flow through a PNP bipolar transistor 95 and the NPN bipolar transistor 92 because the PNP bipolar transistor 94 and the PNP bipolar transistor 95 form a current mirror circuit. Accordingly, based on the temperature at the time, the two-terminal semiconductor sensor device outputs the current flowing through the PNP bipolar transistor 94 and the PNP bipolar transistor 95 as an output current It (see, for example, JP 63-041013 B, FIG. 1).
The external device converts the output current It into a voltage by causing the output current It to flow through a resistor or the like, and the voltage is provided as a measurement value of the sensor.
However, when the resistor or the like for receiving the output current It has low accuracy on the side of the external device that receives the output current It, the output current It may not be accurately converted to the voltage in the external device.